Fluorographene with Narrow Lateral Size and Thickness Distributions Prepared for Enhancing Lubrication Performance of Bentonite Grease

Fluorographene(FG)with narrow lateral size and thickness distributions was prepared by a liquid-phase exfoliation method,based on liquid cascade centrifugation.The Rtec MFT-5000 tribo-meter was used to investigate the lubricating performance of bentonite grease enhanced by the as-prepared FG.The results showed that the coefficient of friction and the wear volume of bentonite grease with 0.3 wt%FG were decreased by 20.4%and 44.9%,respectively,as compared to those of the base grease.The main reason is that FG can promote the formation of the tribo-chemical reaction film consisting of complex carbon oxide,Fe_(2)O_(3)and FeF_(3)on the friction surface,which can remarkably improve the performance of friction reduction and prevent the appearance of severe wear.

Enhancing the Tribological Performance of Conductive Grease Through the Modification of Polypyrrole with Ionic Liquids

This study prepared four types of ionic liquid-modified polypyrrole(IL-modified PPy)as conductive additives and investigated their tribological performance and conductivity in polytetrafluoroethylene lubricating grease.The results indicated that IL-modified PPy effectively enhanced the anti-wear performance and conductivity of the base grease.Among the additives,1-octyl-3-methylimidazolium tetrafluoroborate([OMIm][BF4])modified PPy showed superior performance compared to the other three additives,with the best effect observed at a mass fraction of 0.5%.X-ray photoelectron spectroscopy analysis revealed that IL-modified PPy forms a stable friction chemical film during the friction process,effectively enhancing the lubrication performance and conductivity of the base grease.This indicates broad potential applications in the field of conductive lubrication.

基于ISS-LCG组合特征点的油菜分枝点云配准方法

[目的]针对传统点云配准方法准确率低、速度慢等问题,以油菜Brassica napus L.分枝点云为研究对象,提出基于ISS-LCG组合特征点的配准方法。[方法]以成熟期油菜角果分枝点云为对象,去除背景噪声后,得到清晰完整的油菜分枝点云;然后通过内部形状描述子(Intrinsic shape signature,ISS)提取油菜分枝点云的特征点,再使用线性同余法(Linear congruential generator,LCG)伪随机选取油菜点云的部分点构成关键点,将特征点和关键点进行融合,构成ISS-LCG组合特征点;通过三维形状上下文特征(3D shape context,3DSC)对组合特征点进行特征描述,最后采用RANSAC+ICP两步点云配准法进行点云配准。[结果]基于ISS-LCG组合特征点的点云配准算法以30°为间隔对点云进行两两配准时,配准效果最佳,配准误差约0.066 mm,配准精度比未采用组合特征点的配准方法提升了50%~70%;配准时间均小于48 s,平均配准时间为8.706 s。[结论]该方法在可控环境内可以实现成熟期油菜植株高精度、高效率的自动配准。

Tribological and rheological performance of lithium grease with poly-a-olefin and alkyl-tetralin as base oils

A new category of lithium greases was synthesized by using poly-a-olefin(PAO8) and alkyl-tetralin as base oil, where the alkyl-tetralins were synthesized by the alkylation of tetralin and olefins. The influence of thickener concentration, alkyl-tetralin content and type of blend oils on the rheological and tribological performance of lithium grease was investigated. The microstructures of soap fibers were measured to reveal the structure-property correlations. The concentration of thickener and alkyl-tetralin content obviously affect the lubricating performance of lithium grease, while the molecular structure of alkyltetralin has no obvious impact on their properties. It was found that alkyl-tetralin could significantly enhance the thickening ability of PAO8 base oils, and decrease the amount of thickeners by 1.5%(mass).Lithium greases prepared using 20%(mass) alkyl-tetralin as co-base oil exhibited high colloidal stability,excellent rheological behaviors and tribological properties.

Well-Dispersed Graphene Enhanced Lithium Complex Grease Toward High-Efcient Lubrication

Graphene as a lubricating additive holds great potential for industrial lubrication. However, its poor dispersity and compatibility with base oils and grease hinder maximizing performance. Here, the infuence of graphene dispersion on the thickening efect and lubrication function is considered. A well-dispersed lubricant additive was obtained via trihexyl tetradecyl phosphonium bis(2-ethylhexyl) phosphate modifed graphene ([P_(66614)][DEHP]-G). Then lithium complex grease was prepared by saponifcation with 12-OH stearic acid, sebacic acid, and lithium hydroxide, using polyalphaolefn (PAO20) as base oil and the modifed-graphene as lubricating additive, with the original graphene as a comparison. The physicochemical properties and lubrication performance of the as-prepared greases were evaluated in detail. The results show that the as-prepared greases have high dropping point and colloidal stability. Furthermore, modifed-graphene lithium complex grease ofered the best friction reduction and anti-wear abilities, manifesting the reduction of friction coefcient and wear volume up to 18.84% and 67.34%, respectively. With base oil overfow and afux, well-dispersed [P_(66614)][DEHP]-G was readily adsorbed to the worn surfaces, resulting in the formation of a continuous and dense graphene deposition flm. The synergy of deposited graphene-flm, spilled oil, and adhesive grease greatly improves the lubrication function of grease. This research paves the way for modulating high-performance lithium complex grease to reduce the friction and wear of movable machinery.

Numerical Visualization of Grease Flow in a Gearbox

Lubricating greases are widely used in e.g.open gear drives and gearboxes with difficult sealing conditions.The efficiency and heat balance of grease-lubricated gearboxes depend strongly on the lubrication mechanisms channeling and circulating,for which the grease flow is causal.The computational fluid dynamics opens up the possibility to visualize and understand the grease flow in gearboxes in more detail.In this study,a single-stage gearbox lubricated with an NLGI 1-2 grease was modeled by the finite-volume method to numerically investigate the fluid flow.Results show that the rotating gears influence the grease sump only locally around the gears.For a low grease fill volume,the rotation of the gears is widely separated from the grease sump.For a high grease fill volume,a pronounced geargrease interaction results in a circulating grease flow around the gears.The simulated grease distributions show good accordance with high-speed camera recordings.

Effect of Synthetic Conditions and Thickener Formulation on the Rheological and Tribological Properties of Polypropylene Grease

Polypropylene(PP)grease holds great potential for special industrial applications.In this study,synthetic conditions,thickener content,and the ratio of two different molecular weight PPs were investigated systematically using a rheometer,scanning electron microscope,X-ray diffraction,Fourier transform infrared spectrometer,oscillating tribometer,and 3D surface profiler measurements.The results showed that suitable synthetic conditions are two quenching cycles,and the synthetic temperature and time is 240℃for 12 h.The rheological analysis showed that thickener content and different proportions of the two PP molecular weights have a significant influence on the rheological properties of PP grease.High molecular weight PP(H-PP)has a stronger thickening ability than low molecular weight PP(L-PP).The higher the amount of H-PP in the fixed thickener content or the higher the thickener content with a specific proportion,the higher the viscoelasticity of PP grease.The tribological performance is related to the rheological properties.The proportion of two different molecular weight PPs in the thickener content should be appropriate;excessive H-PP content leads to lubrication failure.

Research Status and Prospects of Bio-based Materials for Grease Barrier Coatings on Paper Food Packaging

Increased environmental and health concerns over the use of plastic packaging or fluorine-containing coatings,in combination with increased market demand for products with a longer shelf life,make bio-based materials one of the most important research candidates for alternative paper packaging materials for oil resistance.These bio-based materials have excellent oxygen and oil barriers,which are critical for food packaging.Moreover,they are biodegradable,naturally renewable,and safe.In this artical,two main groups of bio-based oil repellents for paper food packaging,including polysaccharide-based biopolymers and protein-based biopolymers,are enumerated,and the advantages and weaknesses of bio-based oil repellents are discussed,and effective solutions are proposed.Finally,research status and prospects on the development of bio-based oil-resistant coatings for the food packaging industry are presented.

盾尾刷-油脂腔密封系统油脂逃逸规律研究

油脂逃逸导致油脂腔内压力降低,由此诱发的盾尾密封系统漏水、漏浆等安全责任事故屡屡发生。研制盾尾刷密封系统油脂逃逸的单元体试验装置,采用逐级加压将油脂注入盾尾密封系统油脂腔内,每级压力持续420 s,记录不同盾尾间隙及不同油脂锥入度工况下腔内的密封油脂开始逃逸时的油脂注入压力值、以及逃逸后储油装置中密封油脂的稳定损耗速率,最终获得了盾尾密封系统的油脂逃逸规律,并总结了盾尾油脂的逃逸模式。研究结果表明:1)油脂逃逸速率主要受油脂锥入度和油脂压力的影响,根据油脂逃逸规律变化曲线,油脂逃逸速率可以分为不逃逸、低速逃逸、快速逃逸3个阶段。油脂不逃逸至低速逃逸的油脂压力称为油脂逃逸压力,油脂低速逃逸与快速逃逸之间的油脂压力值为油脂腔内外压差控制值;2)建立了油脂逃逸速率和工程中油脂消耗量的对应关系,结合工程中每环盾尾油脂允许消耗量可实时判断盾尾刷密封性能;3)当油脂锥入度小于286.4(1/10 mm),盾构姿态与管片姿态控制良好时(盾尾平均间隙为75 mm),在水土压力及同步注浆压力基础上最大可增加0.3 MPa的油脂压力,提出的油脂腔内外压差控制值可指导实际工程盾尾油脂压力设定最大值;4)油脂逃逸模式可划分为无逃逸、非均匀逃逸和均匀逃逸3种模式并得出其发生条件。该研究对于指导盾尾密封性的设计及施工有着基础性的意义。

聚脲润滑脂稠化剂对球轴承疲劳寿命的影响

采用光干涉法、动态击穿电压测试对3种聚脲润滑脂样品润滑膜厚进行了表征,同时测试了3种样品的轴承疲劳寿命和温升特性,对比研究了聚脲润滑脂稠化剂对润滑状态的影响,结果表明:聚脲润滑脂稠化剂在摩擦副表面吸附形成垫层,阻碍了润滑脂乏油润滑引起的润滑膜厚持续减小;聚脲润滑脂稠化剂的类型、含量对表面起源型剥落的轴承疲劳寿命有显著影响,合理的稠化剂配方可显著延长轴承疲劳寿命,这可能与聚脲润滑脂稠化剂的回流特性相关。

分形粗糙面的主轴承弹流脂润滑分析

为探究弹性流体动压润滑(弹流润滑)状态下RV减速器主轴承接触表面之间的润滑特性,基于润滑脂的非牛顿特性以及粗糙表面分形理论,提出一种主轴承的点接触弹流脂润滑数值模型。首先,对该模型进行数值求解,得到脂膜压力、脂膜厚度的分布规律;然后,将其分别与其他点接触弹流润滑模型的数值结果和实验结果进行对比,验证了所建模型的正确性;最后,分析了主轴承表面光滑和粗糙状态下流变指数、分形维数、卷吸速度、载荷和润滑脂黏度对润滑性能的影响。结果表明:润滑脂的非牛顿性越明显,脂膜厚度越小且颈缩现象愈加不明显,接触区附近脂膜压力越符合赫兹压力分布,二次压力峰逐渐消失;考虑主轴承分形粗糙表面的弹流润滑特征更切合实际,增大分形维数,接触区真实接触面积增大,有利于降低脂膜压力,增加脂膜厚度;卷吸速度、载荷和润滑脂黏度对脂膜厚度分布的影响显著,对脂膜压力分布的影响较小;脂膜厚度以及最小膜厚越大,主轴承接触区脂膜不易破坏且越容易形成动压润滑。

反向消磁条件下磁流变脂隔震模拟试验研究

采用电磁线圈及永磁体共同控制磁场,自主设计一种可反向消磁的磁流变脂(MRG)剪切试验装置。利用ANSYS Electronics软件对该试验装置磁场分布进行仿真分析,并制备不同羰基铁粉质量分数的MRG,采用振动台对反向消磁条件下MRG的动态剪切性能开展试验测试,分别研究励磁电流、激振幅值和激励频率对MRG动态性能的影响。结果表明:羰基铁粉质量分数对MRG的动态性能影响显著;MRG的剪切应力随励磁电流的增大先快速增大后趋于平缓,阻尼力则逐渐减小;MRG的耗能能力随位移幅值的增加而增强;随着加载频率的增大,其阻尼力略有增加。

风电轴承润滑脂的研究进展

风电轴承的过早失效降低了风机的可靠性,增加了维护运营成本,而轴承性能的优化和可靠性的提高要求润滑脂在各种工况下均能提供理想的润滑性能。总结了风电机组主轴、变桨、偏航和发电机系统中轴承的失效形式,并阐述了润滑脂针对微剥落、微动磨损和电蚀问题的研究进展;对目前风电轴承润滑脂的配方研制和现场试验情况进行了分析总结,其润滑脂普遍采用合成基础油和多种功能添加剂复配协同才能满足润滑要求,现场试验结果表明国产润滑脂性能与在用进口润滑脂相当;润滑脂的组成对风电轴承磨损的影响机制有待进一步深入研究,且应当加快建设自主风电轴承模拟试验台架,为润滑脂的选择提供依据。

含少层石墨烯锂基润滑脂摩擦学与流变学性能研究

为了研究少层石墨烯对锂基润滑脂摩擦学与流变学性能的影响,通过机械搅拌、超声分散及三辊研磨的方式制备不同质量分数的少层石墨烯改性锂基润滑脂,利用MR-10型四球试验机和DHR-2旋转式流变仪分别考察其摩擦学性能和流变学性能。结果表明:少层石墨烯的加入可以有效提高锂基润滑脂的减摩抗磨性能,当少层石墨烯的质量分数为0.1%时效果最佳;少层石墨烯的加入,显著增加了润滑脂流动点对应的应变值和破坏润滑脂皂纤维所需的能量,以及皂纤维结构破坏后恢复所需要的时间。对试验数据进行回归分析,建立基于Herschel-Bulkley模型的不同质量分数少层石墨烯改性锂基润滑脂的流动方程。

磁流变纤维骨架阻尼增强型阻尼器研究

为了增强磁流变脂的剪切性能,提高阻尼器的阻尼力输出,研究棉纤维对磁流变脂剪切增强效果。制备了不同棉纤维质量分数的磁流变脂试样,在流变仪上对其进行测试。结果表明,复合纤维磁流变脂的最大剪切应力随着纤维质量分数的增加而增加。基于复合材料设计制造了一款剪切式磁流变阻尼器,该阻尼器具有磁流变材料用量少、密封要求低等优点。磁流变阻尼器的阻尼特性实验表明,在1.6 A电流下,棉纤维质量分数为1.5%的磁流变脂的最大阻尼力可达99.5 N,与无棉纤维添加的磁流变脂相比,提升了23.8%,这表明使用复合纤维磁流变脂的阻尼器具有更好地阻尼力输出。

不同乳化剂对油脂乳化稳定性的比较研究

乳化剂因其亲水亲油的性质成为制备乳液过程中不可或缺的原料之一,可以降低水的表面张力,帮助不溶于水的物质与水结合,目前对乳化剂乳化能力的研究较少。以大豆磷脂、牛胆盐、蔗糖酯、单甘酯、速能为乳化剂,大豆油、橄榄油、棉籽油为油相,探究不同浓度不同品种的乳化剂对不同油脂的乳化情况,以乳液的分层时间来判断乳液的乳化稳定性。结果表明,在5种乳化剂的处理下,大豆油乳液均表现出良好的稳定性,且其分层时间高于橄榄油和棉籽油。在相同乳化剂处理条件下,随着乳化剂添加量的增加,乳液的稳定时间也呈现逐步增加的趋势。在相同油相不同乳化剂条件下,大豆磷脂具有最长的稳定时间,表现出良好的乳化能力。在乳液制备中大豆油和大豆磷脂具有较好的乳液稳定性,试验结果为食品工业中乳剂的制备和利用提供理论参考。

苦荞叶提取物对油脂的抗氧化能力研究

以DPPH自由基清除率为指标,采用响应面法优化微波提取苦荞叶中抗氧化物质的工艺,并以特丁基对苯二酚(TBHQ)为对照,探究苦荞叶提取物对菜籽油和猪油的抗氧化能力。结果表明:最佳提取工艺条件为提取溶剂为蒸馏水、微波功率400 W、微波时间110 s、微波温度47℃、液料比23∶1(mL/g),在此条件下苦荞叶提取物对DPPH自由基的清除率为80.71%±0.11%。抗氧化试验结果表明,苦荞叶提取物对菜籽油和猪油均具有较好的抗氧化能力。

高真空硅脂的结构研究

文章采用中红外(MIR)光谱技术开展了高真空硅脂的结构研究。研究发现:高真空硅脂结构的红外吸收峰对应的振动模式主要包括CH_(3)不对称伸缩振动(ν_(asCH_(3)-高真空硅脂))、CH_(3)不对称弯曲振动(δ_(asCH_(3)-高真空硅脂))、CH_(3)对称弯曲振动(δ_(sCH_(3)-高真空硅脂))、Si-O伸缩振动(ν_(Si-O-高真空硅脂))、Si-C伸缩振动(ν_(Si-C-高真空硅脂))和CH_(3)面内摇摆振动(ρ_(CH_(3)-高真空硅脂)),高真空硅脂中助剂结构的红外吸收峰对应的振动模式主要包括C=O伸缩振动(ν_(C=O-助剂结构-高真空硅脂))、CH_(2)对称伸缩振动(ν_(sCH_(2)-助剂结构-高真空硅脂))、COO^(-)不对称伸缩振动(ν_(asCOO^(-)-助剂结构-高真空硅脂))。MIR分析证明高真空硅脂与二甲基硅油的结构基本一致。进一步开展了半定量研究,发现高真空硅脂中的助剂主要包括羰基化合物抗氧化剂(相对质量分数约为1.0%)和羧酸盐稳定剂(硬脂酸锂,相对质量分数约为1.4%)。

流动点法表征润滑脂流动性与传统评定方法相关性研究

为建立更完善、高效的轴承润滑脂流动性能评价体系,采用旋转流变仪、润滑脂和石油脂锥入度试验器、润滑脂相似黏度试验器、FFK低温流压仪测试了锂基润滑脂、脲基润滑脂和磺酸钙基润滑脂3种不同稠化剂类型的润滑脂的流动点、锥入度、相似黏度和流动压力,分别研究了锂基润滑脂、脲基润滑脂和磺酸钙基润滑脂3种不同稠化剂的流动点与锥入度、流动点与相似黏度、流动点与流动压力随温度的变化规律并分别计算了它们的皮尔逊相关系数,结果显示润滑脂的流动点与锥入度、流动点与相似黏度、流动点与流动压力具有线性关系,其中流动点与锥入度呈中等相关,流动点与相似黏度、流动点与流动压力呈高度相关,说明利用旋转流变仪测定润滑脂的流动点亦可用于评价润滑脂的流动性能.

热老化下涂覆硅脂对110 kV电缆终端接头界面电-热-力场的影响

为了研究热老化条件下高压电缆终端接头内涂覆硅脂对交联聚乙烯绝缘/硅橡胶绝缘复合界面多物理场分布的影响,采用COMSOL Multiphysics软件建立了110 kV电缆终端接头电-热-力多物理场模型,仿真分析了热老化下涂覆硅脂前后复合界面电场、温度场以及应力场的分布。结果表明:界面涂覆硅脂后,增加了界面的密封性,使界面电场畸变程度减小,界面温升略微下降,但界面应力呈现不均匀分布。老化后,硅脂对硅橡胶的溶胀造成硅橡胶相对介电常数升高,界面电荷密度增大,电场强度进一步增大。温度升高加剧了硅脂对硅橡胶的渗透,使硅橡胶材料热导率降低,界面温度较老化前升高。老化后,涂覆硅脂的硅橡胶弹性模量大幅降低,界面应力进一步减小。